What year were Federal Reserve notes first printed?

The first Federal Reserve notes were printed in the 1914 series.

Denominations were $5, $10, $20, $50, and $100. They were printed with both red seals and blue seals; green wasn't adopted as the standard seal color until 1928. In general, 1914-series FRNs with red seals are worth several times the value of their blue-seal counterparts.